Osteoporosis is a disease that leads to defective skeletal function caused by low bone mass and deterioration of bone quality. In this respect, bone characterized by weakened mechanical strength is much more susceptible to fracture, even under stresses that would otherwise be tolerated by normal bone. In the United States alone, some 8 million women and 2 million men suffer from osteoporosis. Many more are at increased risk for osteoporosis because they have low bone mass. The risk of suffering from osteoporosis increases with age, particularly in those over the age of 50.
Osteoporosis results from a disorder in bone remodeling, which is the process by which bone tissue is continually renewed and repaired. In bone remodeling, osteoclasts resorb old or damaged bone, while osteoblasts synthesize a new bone matrix. In patients who suffer from osteoporosis, the rate of bone resorption undesirably exceeds the rate of bone formation, either because too much bone is resorbed or too little bone is formed.
Drugs used in the treatment of osteoporosis act by inhibiting bone resorption. Among such anti-resorptive agents are bisphosphonate compounds. Bisphosphonates are synthetic analogues of pyrophosphates, which are naturally occurring regulators of bone turnover.
Bisphosphonates, like pyrophosphates, can bind to the surface of the hydroxyapatite bone matrix. It will be appreciated by the ordinarily skilled artisan that the pharmacologic properties of bisphosphonates can be varied through side chain substitutions (R1, R2) on their general chemical structure. For example, alendronate has an amino side chain (R2═CH2CH2CH2NH2) while risedronate has a cyclic nitrogen-containing side chain. The R1 and R2 side chains for a variety of bisphosphonate compounds are given in Table 1.
TABLE 1BisphosphonateR1 side chainR2 side chainEtidronateOHCH3ClodronateClCIPamidronateOHCH2CH2NH2AlendronateOH(CH2)3NH2RisedronateOHCH2-3-pyridylTiludronateHCH2-S-phenyl-ClIbandronateOHCH2CH2N(CH3)(pentyl)ZoledronateOHCH2-imidazoleYH529OHCH2-2-imidazopyridinylIncadronateHN-(cycloheptyl)OlpadronateOHCH2CH2N(CH3)2NeridronateOH(CH2)5NH2EB-1053OHCH2-1-pyrrolidinyl
The oral administration of bisphosphonate compounds for the treatment of osteoporosis suffers from several major drawbacks. First, bisphosphonate compounds are very poorly absorbed from the gastrointestinal tract into the blood of a patient (e.g., have low bioavailability). In fact, typically only about 0.5% to about 5% of the total bisphosphonate active ingredient is absorbed from an oral dosage formulation (e.g., a solid tablet). Once in the blood stream, typically only about 20% to about 50% of the bisphosphonate becomes bound to the bone surface. The bioavailability of bisphosphonate is further reduced under highly acidic gastric conditions, which occur when the patient has eaten food or consumed an acidic beverage (e.g., coffee, tea, or orange juice).
The bioavailability of the bisphosphonate is further affected by the delivery system. Solid delivery systems such as capsules and tablets must be ingested with sufficient liquid to disintegrate the dosage form. Once the dosage form is inside the stomach or small intestine of a patient, it has to disintegrate into small particles, and the active ingredient has to be solubilized such that it can be absorbed into the plasma of the patient. The disintegration and solubilization processes for solid dosage forms delay the bioavailability of the active ingredient.
Effervescent drug formulations can offer enhanced dissolution and absorption of active ingredients resulting in increased bioavailability. Frequently, active ingredients are absorbed better from effervescent formulations as compared to dry, solid tablet formulations. Effervescent tablets also can be larger in size allowing for higher drug loading as well as combination drug loading. Because the tablets are dissolved in water, they are easier to swallow than dry solid tablet formulations. Furthermore, effervescent compositions can be formulated without polyvalent metal ions (e.g., Ca2+ and Mg2+), which can bind to bisphosphonate compounds rendering them insoluble and unabsorbable. An effervescent bisphosphonate composition is disclosed in U.S. Pat. No. 5,853,759 which describes an effervescent tablet comprising a bisphosphonate, in particular alendronate, an acid component, and an alkaline effervescing component.
A second drawback, even with effervescent formulation, often encountered by patients taking regular dosages of bisphosphonates is the common occurrence of upper gastrointestinal disturbances. Such disturbances include heartburn, esophageal irritation, and even, in some cases, esophageal ulcers. The local tissue irritation and ulceration associated with the administration of bisphosphonates may be mitigated by the administration of drugs that suppress gastric acid production. Anti-ulcer agents such as H2-antagonists (i.e., histamine H2-receptor antagonists) and proton pump inhibitors are known to be effective in combating acid-peptic diseases. Proton pump inhibitors (e.g., H+, K+-ATPase inhibitors) are α-pyridylmethylsulfinyl benzimidazole compounds having different pyridine or benzimidazole substituents. The proton pump inhibitors react with acid (are activated) to form thiophilic sulfenamide or sulfenic acid components. Once activated, the compounds irreversibly bind to the sulfhydryl group of cysteine residues thus halting acid production. Commercially available H2-antagonists include cimetidine (Tagamet®), ranitidine (Zantac®), famotidine (Pepcid®), and nizatidine (Axid®). The H2-antagonists inhibit acid production by competing with histamine in binding to H2-receptors.
The combination of these problems has led to a complicated regimen that attempts to optimize bioavailability of the bisphosphonate while minimizing the gastrointestinal problems. Thus, current regimens require the patient to (a) remain strictly upright for at least 30 minutes after taking the bisphosphonate composition so as to minimize esophageal irritation, and (b) wait as much as 2 hours before eating.
U.S. Pat. Nos. 5,994,329, 6,015,801, 6,225,294, and 6,333,316 as well as EP 1 127 573 A1 disclose methods for inhibiting bone resorption comprising sequential administration of histamine H2 receptor blockers and/or proton pump inhibitors about 30 minutes to about 24 hours prior to administration of bisphosphonates. Administration of such histamine H2 receptor blockers and/or proton pump inhibitors in this manner exacerbates the already complicated and inconvenient regimen because the patient would have to take the histamine H2 receptor blockers and/or proton pump inhibitors (e.g., upon waking), then wait 30 minutes or longer to take the bisphosphonate and then wait up to 2 more hours to eat.
Despite the availability of the foregoing approaches, it will be appreciated that there remains a need in the art for compositions and drug administration regimens for osteoporosis, or other bone resorption disorders, which are less complicated and more convenient than those commonly known in the art. Moreover, there remains a need for a composition that can deliver a bisphosphonate drug for treating osteoporosis (or other bone resorption disorders) while reducing associated ulceration. The invention seeks to provide such compositions to satisfy at least one of these needs. These and other advantages of the invention will be apparent from the description of the invention provided herein.